1. Field of the Invention
The invention relates to filled organic polymeric compositions with enhanced toughness and stiffness, improved surface appearance, reduced coefficient of expansion, increased abrasion resistance, improved melt characteristics for processability, improved retention of optical properties, dyeability, and reduction of static charge retention. More particularly, the invention is of composites including an organic polymeric matrix randomly filled with submicron sized particulates having a BET specific surface area greater than about 200 m.sup.2 /g, a substantial proportion of which particulates are present in the matrix at the fundamental particle size.
2. Description of the Related Art
Various particulate fillers and extenders have been incorporated into polymers for numerous reasons, such as providing or modifying physical properties, chemical properties, visual properties, or cost-effectiveness. Among the polymer properties which can be provided or modified by particulate fillers are opaqueness, density, color, toughness, strength, modulus, fire-retardency, aesthetic appearance, and polymer morphology such as crystallite formation.
According to Brydson, "Plastics Materials," Third Edition, pp. 114-117 (1975), the term "filler" is usually applied to solid additives incorporated into a polymer to modify its physical (usually mechanical) properties. Particulate fillers are divided into two types: inert fillers and reinforcing fillers. The term "inert filler" is said to be a misnomer because many properties may be affected by incorporation of such a filler. As an example, in a plasticized polyvinyl chloride compound, the addition of an inert filler will reduce die swell on extrusion, increase modulus and hardness, and may provide a white base for coloring, improved electrical insulation properties and reduce tackiness. It is stressed that in each chemical type of filler, a number of grades are available. These grades differ in the following ways: average particle size and size distribution; particle shape and porosity; chemical nature of the surface; and impurities, such as grit and metal ions.
Brydson indicates that the chemical nature of the filler surface has a "vital effect." Mineral fillers often have polar groups, for example, hydroxyl groups, which render them attractive to water but not to organic polymers. To improve the wetting of polymers to fillers, and hence obtain better products, mineral fillers are often pretreated. For example, calcium carbonate may be treated with stearic acid, the acid group attaching itself to the filler particles while the aliphatic chain is compatible with the polymer. Besides improving wetting, such treatment can have a second function: surface hydroxyl groups tend to hydrogen bond to other additives, such as anti-oxidants and some cross-linking components making them ineffective. Preferential absorption by a less expensive additive, such as a glycol, can give much improved results. Coupling agents have been developed, such as certain silanes, which in effect form a polymer shell around the surface of the particle and improve wetting to the main polymer.
Aside from the inert fillers, reinforcing particulate fillers are effective primarily with elastomers although they can cause an increase in tensile strength with plasticized polyvinyl chloride. By mixing carbon black into styrenebutadiene rubber, tensile strength can be increased to over 20 MN/m.sup.2 from a strength of about 3 MN/m.sup.2. Reinforcement appears to depend upon three factors: an extensity factor (relating to the total amount of surface area of filler per unit volume in contact with the elastomer); an intensity factor (the specific activity of the filler-polymer interface causing chemical and/or physical bonding); and geometrical factors (such as structure or aggregation and porosity of the particles).
Rubbery materials are often incorporated into rigid amorphous thermoplastics to improve their toughness. However, it is not clear whether they should be referred to as "rubbery fillers." Likewise, rubber technologists often incorporate synthetic resins or plastics into the rubbers. Further, fibrous fillers have long been used in plastic materials. These include wood flour, cotton flock, mascerated fabric, short lengths of synthetic organic fibers such as nylon, asbestos, glass fiber, chalked carbon fiber, and the like.
It is an existing problem in the art that for many of the combinations of polymer matrix and crystalline fillers, the fillers were not and could not be dispersed at the primary particle level,. i.e., the extensivity factor is below the optimum achievable when maximum use is made of the surface area per unit volume of filler to contact polymer. Thus composite performance attributes could not be maximized. For example, U.S. Pat. No. 4,727,167 teaches that lithium aluminates can be added to polymers, waxes and paraffins which can be sufficiently fluidized to permit adequate mixing. However, it is nowhere stated that these lithium aluminates were dispersed at the primary particle level.
U.S. Pat. Nos. 4,085,088; 4,284,762; 4,299,759; 4,351,814; 4,629,626; and 4,686,791 assigned to Kyowa Chemical Industry Co., Ltd. disclose the use of a hydrotalcites, some having a specific surface area of not more than 30 m.sup.2 /g, as determined by the BET method. One hydrotalcite is of the general formula EQU Mg.sub.1-x Al.sub.x (OH).sub.2.A.sub.x/n.sup.n-.mH.sub.2 O
wherein x is a member of more than 0 but up to 0.5, A.sup.n - represents an anion having a valence of n, preferably a divalent anion such as CO.sub.3.sup.2- or SO.sub.4.sup.2-, and m is a positive number. The hydrotalcite preferably has a &lt;003&gt; crystallite size of at least 600 angstroms, especially 100 angstroms. These hydrotalcites are distinguishable from ordinary hydrotalcites that have a BET specific surface area of at least 50 m.sup.2 /g. The original hydrotalcites have a &lt;003&gt; crystallite size of not more than about 300 angstroms. Also disclosed in the '814 patent are fibrous hydrotalcites having a hexagonal needle-like crystal structure, that is produced by contacting a basic magnesium compound having a needle-like crystal structure, expressed by the formula: EQU Mg(OH).sub.2-n'x2 A.sub.x2.sup.n-.m.sub.2 H.sub.2 O
wherein A.sup.n'- represents a monovalent or divalent anion, n' is 1 or 2, and x.sub.2 and m.sub.2 are numbers satisfying the following conditions: EQU 0.2.ltoreq.x.sub.2 .ltoreq.0.5, EQU 0.ltoreq.m.sub.2 .ltoreq.2,
with a compound capable of providing a trivalent metal cation (M.sup.3+) and being soluble in a liquid reaction medium which is chemically inert and is a non-solvent for the basic magnesium compound. The contacting being carded out in said liquid reaction medium under conditions which do not cause a loss of the needle-like crystal form of the basic magnesium compound, while maintaining the ratio of M.sup.3+ to the sum of Mg and M.sup.3+ at 0&lt;M.sup.3+ /(Mg+M.sup.3+).ltoreq.0.6 and the pH of the contacting system at not less than 9.
U.S. Pat. Nos. 4,889,885 and 5,102,948 relate to composite materials containing layered silicates. These silicates are anionic fillers and are assertedly uniformly dispersed at high content in a polyamide matrix. In order to produce such a composite, a layered silicate, with a cation exchange capacity of 50 to 200 millieqivalents per hundred grams (meq/100 g) is placed in a swelling condition in a dispersion medium and admixed with a polyamide resin for about 30 minutes or less. This results in a composite in which the layered silicate is uniformly dispersed. When the swellability of the layered silicate and dispersion medium is very good, the layered silicate will apparently be "ultra finely dispersed" in the dispersion media and will not settle out by gravity. The dispersion mediums include water, methanol, ethanol and/or .epsilon. caprolacam, among others. The '885 patent utilizes a resin other than polyamide resin and layered silicates with a layer thickness of from about 7 to about 12 angstroms, with an inner layer distance of 30 angstroms or above. It is asserted that the uniform dispersion of the layered silicate in the resin results in superior mechanical characteristics, heat resistance, water resistance, and chemical resistance.
There yet exists a need for a composite with a filler that can be dispersed at the primary particle level in the organic polymeric matrix to permit optimization of extensivity-related composite performance attributes. There yet exists a need for a filled organic polymeric composite that retains toughness and improves stiffness, that has good surface appearance, that has a reduced coefficient of expansion, that has enhanced abrasion resistance, that has flame retardancy, that has improved melt characteristics for processability (such as blow molding), that retains its optical properties, that is dyeable, and that has an improved capability to dissipate static charges.